The present invention relates to an ignition system for a motor vehicle and a method for operating an ignition system of a motor vehicle.
In ignition systems for motor vehicles, a magnetic field may be generated in an ignition coil by a primary current and may then be momentarily switched off, as a result of which the magnetic field may break down and, in the ignition coil functioning as transformer, a high secondary voltage may be generated that may result in the production of the ignition spark in the spark plug of the secondary current circuit. However, it may be problematic that when the primary current is switched on, or started up, a secondary voltagexe2x80x94having the opposite sign of the desired ignition voltagexe2x80x94may be induced, which, as a closing spark (energizing spark), may lead to the generation of a spark at the spark plug.
This potential ignition from a closing spark may have different significance in the different ignition systems. In ignition systems, whose primary circuit is supplied by the vehicle power supply source, i.e., the vehicle battery, some 100 xcexcs may be required in order to build up the magnetic field at sufficient energy for the initiation and maintenance of the ignition process during the desired ignition duration. Therefore, ignition from the closing spark may still occur in the compression phase, perhaps while the intake valve is open, and may have serious consequences. Because the induced cut-in (sealing) voltage may have the opposite polarity from the ignition voltage that is induced in response to the breakdown of the magnetic field, a closing spark may be effectively suppressed using a CSS (closing-spark-suppression) diode in the secondary circuit.
In an AC ignition (ACI) system, the primary current circuit may be supplied with high voltage from an energy source, greater than 150 V for example, for which purpose a complex and expensive transformer may be required. A comparatively shorter drive signal that is emitted at a later point in time may bring about, in a functional device, the generation of a plurality of short, sequential pulse packets, which may drive the ignition transistor and which may create in the primary current circuit a sequence of essentially saw-tooth-shaped current pulses. Because the charging process in ACI may be short and may begin late, a pre-ignition from the closing spark may only result in the ignition process commencing somewhat earlier than an ignition that occurs in response to the immediately following voltage drop of the first pulse. Therefore, in an ACI, a CSS diode may not be required. As a result of the plurality of sequential primary current pulses and the secondary current pulses that are induced therefrom, energy may be fed continuously to the spark plug even after the commencement of the ignition, so as to make available sufficient energy over the ignition period.
However, in the ACI, the use of the complex and expensive transformer may be undesired. Furthermore, expensive components such as capacitors and power switches may be required in the secondary current circuit for voltages over 1000 V.
In a pulse train ignition (PTI) just as in an ACI, the ignition transistor is driven by a functional device having a timing element, as a result of which in the primary current circuit a sequence of essentially saw-tooth-shaped, or trapezoidal, current pulses may be generated. However, because the primary current circuit, just as in the case of other ignition systems, is applied with power from the vehicle battery, i.e., the vehicle electrical system, the charging process of the ignition coil may be significantly lengthened by the primary current circuit in comparison to the ACI, so that an ignition by the closing spark during the compression stroke may have catastrophic consequences, such as, for example, when the intake valve is open. Therefore,xe2x80x94just as in the case of other ignition systems without a pulse sequencexe2x80x94a CSS diode may be connected in the secondary current circuit so that a closing spark that is induced in response to the start-up of the primary current may be blocked in the secondary current circuit, and the ignition current may be let through that is induced in the secondary current circuit in response to the sudden voltage drop after the first primary current pulse.
However, when the CSS diode is used in the secondary current circuit, the secondary voltage pulses that are induced by the succeeding primary current pulses may only be partially relayed to the spark plug as secondary current pulses. The CSS diode may only admit current pulse packets that have the same polarity as the ignition voltagexe2x80x94i.e., during the blocking period of the ignition transistorxe2x80x94so that the energy supply to the spark plugs may be significantly reduced and may be interrupted over time, as a result of which it may become more difficult to maintain the ignition spark over the desired spark period.
According to an exemplary ignition system and exemplary method for operating an ignition system, the closing spark may be reliably suppressed and nevertheless a high energy supply may be assured to the spark plug during the ignition process. This may be achieved on the basis of relatively low effort and cost.
According to an exemplary embodiment and/or exemplary method of the present invention, in the secondary current circuit a component may therefore be used that reliably suppresses a closing spark during the initiation of the charging process, since previously no voltage was applied at the component in the through direction, and therefore no forward current was flowing. Subsequently, in response to the falling edge of the primary current and the breakdown of the magnetic field of the ignition coil, the induced ignition current may be reliably let through in the forward direction, as a result of which the component is permeated by charge carriers. If the ignition spark is burning and the ignition transistor is once again switched on, the componentxe2x80x94other than in a pulse train ignitionxe2x80x94may remain conductive even during the recharge period, in response to voltage that is originally applied in the blocking direction.
In this manner, on the one hand, a reliable functioning of the ignition system may be assuredxe2x80x94suppressing the closing spark and letting through the ignition sparkxe2x80x94and, on the other hand, the energy supply to the spark plug may be maintained during the recharge period.
According to an exemplary embodiment of the present invention, any component that has the desired properties may be used as the component. In particularxe2x80x94but not exclusivelyxe2x80x94this component may be a break-over diode or triac (bidirectional thyristor triode). In this context, the triac may be connected as a diode (transistor diode), in that its gate is connected to a main electrode and therefore may form the anode.
The component according to an exemplary embodiment of the present invention may therefore differ in principle from the diodes that are used in other prior systems for suppressing closing sparks, that only have a capacitative behavior but that do not let through sufficient current in the blocking direction for maintaining a spark current. According to an exemplary embodiment and/or exemplary method of the present invention, the minimum hold-off interval of the component may be larger than the period of the secondary voltage increase after the ignition transistor is once again connected (or switched on).
According to an exemplary embodiment and/or exemplary method of the present invention, therefore, in the secondary current circuit a component may be used that is fundamentally a blocking-type one but that is sufficiently slow-acting from the point of view of dynamic behavior, whose properties may be matched to the dimensioning of the ignition coil and to the system voltage used, such that the recharge pulses are let through, but no charge carriers remain after the termination of the ignition process until the commencement of the next ignition process, so that the generation of a closing spark may be reliably prevented in response to a subsequent buildup of the primary current.
In contrast to an AC ignition, the complex and costly transformer for generating a higher voltage for the primary current circuit may be omitted. Furthermore, using the component, a more reliable determination of the commencement of the ignition process may be provided than in the case of an ACI, because the ignition may not be produced by the closing spark. In this context, the extra expense of the component, such as, for example, when a triac or a break-over diode is used, may be small in comparison to an ACI.
In comparison to pulse train ignition, an open energy supply to the spark plug may be provided, the overall energy supply may be significantly increased, and therefore the ignition process may be improved. Furthermore in the ignition system according to an exemplary embodiment of the present invention, the polarity of the secondary voltage may be changed, so that the firstxe2x80x94and therefore most powerfulxe2x80x94secondary current may not result in increased burnup in the spark plug, and an ion current evaluation may be performed, if it is employed, using a positive measuring voltage.